The objectives of this study are: Phase I - the examination of temporal trends in incidence rates of aplastic anemia (AA) and acute nonlymphocytic leukemia (ANLL; Phase II - examination of the role of environmental agents in AA and ANLL by means of a case-control epidemiologic investigation. Phase I of the study is almost completed. Thus far, 140 cases of AA and 723 cases of ANLL have been identified through a hospital record search. Death certificate search is underway and should help to ascertain additional cases. Additionally, a search will be carried out of hospital records at the NIH Clinical Center, in order to identify possible cases who may have sought care in the D. C. area. Phase II of the study will start in December, 1980. Procedures for the collection of data, as well as selection of controls, have been designed.